1. Technical Field
The present invention relates in general to storage systems, and in particular disk drives. Still more particularly, the present invention relates to a method for controlling the temperature of a disk drive during testing using the disk drive's own hardware and sensors.
2. Description of the Related Art
A hard disk drive (HDD) is a digital data storage device that writes and reads data via magnetization changes of a magnetic storage disk along concentric tracks. The HDD is tested before being shipped to the customer. In addition, the customer often tests the HDD on a periodic basis after the HDD is operational. The HDD can be tested either for on/off failures or for gradual performance degradation.
On/off failures are failures in which an item fails, such as a cable breaks, a disk does not spin, a read/write head does not function at all, etc. Such failures are easy to identify and locate, but may require putting the HDD in an artificial condition, such as temperature extremes, high vibration, etc., that makes such an on/off failure more likely. Such conditions can cause undetected damage to the HDD, and thus on/off failure analysis has inherent limitation.
Gradual performance degradation occurs before an on/off failure. While such performance degradation may be caused by the same conditions that cause an on/off failure, evaluation of gradual performance degradation is typically performed under conditions much less severe than those that may cause an on/off failure.
Data produced by gradual performance degradation is used to conduct a predictive failure analysis. The gradual performance degradation data can be extrapolated or otherwise manipulated/evaluated to predict an ultimate on/off failure, or else an unacceptable performance degradation. This type of data extrapolation is referred to as Predictive Failure Analysis (PFA). PFA evaluates performance using either a “symptom driven” process or a “measurement driven” process.
The symptom driven process evaluates error logs. That is, when a failure in disk rotation speed, data read/writes, noise reduction, etc. occurs, an error log is generated, allowing the tester to identify the cause of the problem. Such a process is similar to an on/off failure analysis, except that the HDD has not entirely failed; rather only a partial function of the HDD has failed.
The measurement driven process detects Generalized Error Measurements (GEM), which detects changes in performance, although not necessarily functional errors. That is, a GEM may detect an increase in the distance between a read/write head and a disk surface, or an increase in noise in a digital signal read by the read/write head, but such increases do not cause a failure of the entire HDD or an HDD component, and thus are not considered “errors.” Nonetheless, such GEMs are good indicators of potential problems, especially if the conditions causing the GEMs are allowed to persist or increase. For example, if the distance between the read/write head and disk surface (known as the “flying height” of the head) increases beyond an expected tolerance as the operating temperature of the disk surface increases, then a failure can be predicted if the temperature continues to rise beyond the normal operating temperature or remains at the normal operating temperature for an extended period of time.
Test condition parameters, including temperature, required during the detection of GEMs are established by a test engineer. For example, the test engineer may write a test program that measures flying height when the disk drive is operating at 30° C.±4°. In order to keep the HDD at or near this range of temperatures, various methods are used in the prior art. Most such methods include test bench heating or cooling devices, which force regulated hot or cold air across or into the HDD until the desired test temperature condition is reached. Such heaters/coolers require additional test bench footprint space, electrical outlets, feedback controls, and cost.
In addition, an operations computer may test its HDD periodically. Such testing also requires the temperature of the HDD to be within pre-determined levels during testing, typically, using the HDD's on-board cooling system (fan). However, such fans can only cool, not warm up the HDD.
What is needed, therefore, is a method for regulating the temperature of an HDD, which is being tested, without the need for and use of additional hardware.